Sensor housing with process terminal

ABSTRACT

A two-part housing (1) for pressure sensors, with a bottom part (2) as the process connection and a top part (3) as the component receiver which contains at one-half of the electrical and electron components. Joining of the bottom part (2) and the top part (3) of the described housing (1) is especially simple and reliable in that the bottom part (2) and the top part (3) are connected to one another by an elastic press fit and in the area of the press fit there are straight surfaces (6) and curved surfaces (7).

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a two-part or multipart housing for sensors,especially pressure and flow sensors, with a bottom part as the processconnection and a top part as the component receiver which thereforecontains most or all of the electrical and electronic components.

Sensors which are used to monitor a medium or the property of a medium,for example, the pressure of a liquid or a gas, consist generally of atleast two parts, the bottom part being connected to a container or pipewhich carries the medium, and therefore often also being called theprocess connection. These sensors are mainly pressure or flow sensors,but can also, for example, be capacitive fill level sensors. In thesesensors, the housing is used, on the one hand, like all sensors, toprotect the sensor and the associated electronics, but on the other,also for reliable and permanent connection to the medium-carrying pipeor container.

The advantage of a sensor with a two-part or multipart housing is that,when there is a defect of the sensor or electronics, only the upper partof the housing, need be replaced without the need to intervene in therunning process by replacing the process connection. But in thesehousings, one problem is the connection between the bottom part which isused as the process connection and the top part which contains the bulkof the electronics and which often has a plug or cable connection forthis purpose.

In the known housing of the initially mentioned type, the processconnection consists of nickel-plated brass. It is produced by turningfrom standardized hexagonal solid material, part of the originalhexagonal surface being maintained as a key surface. For connection tothe measurement medium it has an inside or an outside thread. The bottompart of the housing is connected to the top part by a press fit,knurling being formed on the top end of the bottom part. The wallthickness of the top part which is made as a pipe section, for costreasons generally as a welded pipe section, decreases gradually in thedirection to the knurling.

The disadvantage in this known housing is that by pressing the top partonto the bottom part the protective nickel layer is partially damaged inthe area of the knurling and the underlying brass is not very resistantchemically. This is especially disadvantageous when the measurementmedium is chemically corrosive. Another major disadvantage is that withregard to the inside diameter of the top part and the outside diameterof the bottom part in the area of the press fit only very smalltolerances are allowable. The forces to be expended for the press fitand the loading capacity of the connection depend largely on thesetolerances. Since the wall thickness of the top of the press fit is verylow, cracks or deformations of the top part can occur.

Housings of the above described type are also known in which the toppart and the bottom part of the housing are welded or screwed to oneanother. If the top part and the bottom part are welded together, ofcourse the electronics can no longer be replaced without intervening inthe process. Since the electrical connection, which is often aplug-and-socket connection, is very short between the top part and thebottom part, due to improper screwing and overly large tolerances of thethreads a displacement of the top part relative to the bottom part canoccur which can no longer ensure reliable operation of the sensor.

SUMMARY OF THE INVENTION

The object of the invention is to make available a housing in which theconnection between the top and bottom part can be effected easily, butalso reliably.

The aforementioned object is achieved in accordance with the inventionby the bottom part and the top part being connected to one another by anelastic press fit, and in the area of the press fit, there beingstraight surfaces and curved surfaces. By means of the elastic press fitand the different surfaces, the tolerances of the inside diameter andthe outside diameter of the top and bottom part need not be madeespecially narrow; this leads to economical production. For the sametolerances as in the prior art, the probability of damage to the top andbottom part is clearly reduced.

The straight and curved surfaces are located preferably in the top areaof the bottom part and there they form a press fit surface. When the toppart and the bottom part are joined, the top part in the area of thecurved surfaces then adjoins the bottom part, while in the area of thestraight surfaces it adjoins the bottom part only slightly or not atall, so that a free space is formed between the top part and the bottompart. The top part can thus deform in the direction of the straightsurfaces without cracks forming.

According to one advantageous embodiment of the invention, on the bottompart underneath the press fit surface there is a groove for holding anO-ring. This O-ring is used for additional sealing of the housing sothat neither liquid nor dirt can enter the housing at the connectingpoint between the top part and bottom part.

To further facilitate joining of the top part and bottom part of thehousing, in the housing in accordance with the invention the top edge ofthe bottom part can be made as an insertion cone above the press fitsurface. Joining of the top part and bottom part can be furtherfacilitated by the wall thickness of the top part decreasing in thepress fit area. In doing so the decrease of the wall thickness can takeplace both incrementally or also continuously in the direction to thelower part.

To facilitate attachment of the bottom part to a process line or a tank,part of the bottom part is made, for example, as a hexagonal keysurface. This key surface can advantageously contain a graduation whichis used as the support surface for the lower edge of the top part.

If the bottom part is produced by turning from standardized hexagonalsolid material, advantageously one part of the original hexagonalsurface can be used as the key surface. In addition, part of theoriginal hexagonal surface can be taken over as straight surfaces of thepress fit surface. But of course, the key width of the straight surfacecan also deviate from the key width of the key surface. Likewise,instead of the solid hexagonal material a square bar material with aquadratic cross section or some other bar material with a regularpolygonal cross section can be used.

The top part which is advantageously produced from a welded sleeve canhave both a constant outside diameter and also an outside diameter whichwidens to the top. Advantageously, the top part also has a hole for aplug connection.

For very small wall thicknesses of the top part, for additional fixingin addition to the elastic press fit, there can also be a catchconnection between the bottom part and the top part.

Both the top part and also the bottom part of the housing advantageouslyconsist of coated brass, for example, nickel-plated brass, or ofuncoated high quality steel, for example, V4A.

In particular there are a host of possibilities for developing thehousing in accordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a housing of a sensor with an additional housing head,

FIG. 2 shows one version of a bottom part of a housing in accordancewith the invention in a side view,

FIG. 3 shows the bottom part as shown in FIG. 2 as a cross section alongline A--A in FIG. 2,

FIG. 4 shows the bottom part as shown in FIGS. 2 and 3 as a longitudinalsection along line B--B in FIG. 3,

FIG. 5 shows one embodiment of a top part of the housing in accordancewith the invention in a longitudinal section and

FIG. 6 shows the bottom part as shown in FIGS. 2, 3 and 4 and the toppart as shown in FIG. 5 joined as one preferred embodiment of a housingin accordance with the invention with an additional plug-and socketconnection.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a multipart housing 1 consisting of a bottom part 2 and atop part 3. The housing 1 is sealed by a housing head 4 which has ameasured value display 5.

The bottom part 2 which belongs to the housing 1 in accordance with theinvention, as FIGS. 3 and 6 show, has straight surfaces 6 and curvedsurfaces 7 which together form a press fit surface 8 (compare FIGS. 2and 4). After joining the bottom part 2 and the top part 3, the topparts 3 lies in the area of the curved surfaces 7 on the bottom part 2,while in the area of the straight surfaces 6 there is a free space 9between the top part 3 and the bottom part 2. Under the press fitsurface, in the bottom part 2 there is a groove 10 into which an O-ring11 fits to seal the bottom part 2 relative to the top part 3. Above thepress fit surface 8 is an insertion cone 12 with a diameter whichdecreases in the direction of the top edge of the bottom part 2. Thisinsertion cone 12 facilitates pressing the top part 3 over the press fitsurface 8. Under the groove 10 is a hexagonal key surface 13 with sixcorners in the upper area each having a graduation 14. The graduations14 are used as a support surface for the lower edge of the top part 3which is pressed over the insertion cone 12, the press fit surface 8 andthe groove 10, with the O-ring inserted therein. In the housing shown inFIG. 1, the bottom part 2 and the top part 3 are joined so that thelower edge of the top part 3 is directly adjoined by the key surface 13of the bottom part 2.

FIG. 3 shows the bottom part 2 as shown in FIG. 2, but here in crosssection along the line A--A so that the aforementioned straight surfaces6 and the curved surfaces 7 of the press fit surface 8 become apparent.FIG. 3 also shows that the straight surfaces 6 have the same key widthas the key surface 13. The bottom part 2 shown has been produced byturning from standardized solid hexagonal material. Here, both for thestraight surfaces 6 and also for the key surface 13, the shape of theoriginal solid hexagonal material has remained unchanged.

Since the bottom part 2 is the process connection of a pressure sensor,the bottom part 2 in the lower area has an inside thread 15 and anoutside thread 16, and in the upper part, an inside thread 17. The lowerarea of the bottom part 2 therefore enables both the bottom part 2 to bescrewed into a pipe or a container, in conjunction with a correspondinginside thread of the pipe or tank, and also screwing onto a pipeprovided with a corresponding outside thread. The inside thread 17provided in the upper area of the bottom part 2 is used to hold asupport ring which is provided with a corresponding outside thread andwhich is assigned to a pressure measurement cell.

FIG. 4 shows the bottom part 2 as shown in FIGS. 2 and 3 in alongitudinal section along line B--B in FIG. 3. FIG. 4, like FIG. 2,shows the insertion cone 12 located above the press fit surface 8. Theinside thread 17 extends over the height of the insertion cone 12, thepress fit surface 8 and the groove 10.

FIG. 5 shows the top part 3 of a housing 1 in accordance with theinvention in a longitudinal section. The top part 3 has the shape of asleeve with an outside diameter 18 constant over the length. In thelower area of the top part 3 is a press fit area 19 which, upon joiningto the bottom part 2, is pressed over the press fit surface 8 of thebottom part 2 and which has a lower edge which sits on the graduations14 of the bottom part 2. The wall thickness of the press fit area 19decreases in steps toward the lower edge of the top part 3. The decreaseof the wall thickness in the press fit area 19 facilitates pressing thetop part 3 onto the bottom part 2. The wall thickness can of course alsodecrease in some other way, for example, continuously. Likewise, inanother version of the top part 3 its outside diameter 18 can change,for example, can widen to the top. On one side of the top part 3, in itsupper area, there is a hole 20 which is used to hold a plug connection21 shown in FIG. 1. In the bottom part of the press fit area 19 of thetop part 3, there is an O-ring area 22 which in the joined state of thebottom part 2 and the top part 3 surrounds the groove 10 of the bottompart 2. Thus, then, the O-ring is pressed between the groove 10 of thebottom part 2 and the O-ring area 22 of the top part 3 so that areliable seal is achieved.

It has been stated above that the bottom part 2 has been produced byturning from standardized solid hexagonal material. Here, the corners 23which were originally present and which are shown in FIG. 6 have beenrounded off. The outside diameter 24 of the key surface 13 correspondsto the outside diameter 18 of the top part 3.

As can be taken from FIG. 5, the part of the top part 3 away from thebottom part 2 is provided with an end area 25 with a wall thicknesswhich is diminished incrementally towards the top. The end area 25 ofthe top part 3 is used to hold the housing head 4 shown in FIG. 1.

FIG. 6 shows the housing 1 as claimed in the invention, the top part 3as shown in FIG. 5 being pressed onto the bottom part 2 as shown inFIGS. 2 to 4. FIG. 6 also shows the plug connection 21 which is attachedin the hole 20 of the top part 3. FIG. 6 again shows the straightsurfaces 6 and the curved surfaces 7 of the bottom part 2, the top part3 in the area of the curved surfaces 7 of the bottom part 2 adjoiningthe latter and in the area of the straight surfaces 6 of the bottom part2 a free space 9 can be recognized between the top part 3 and the bottompart 2. The top part 3 can deform in the direction toward the straightsurfaces 6 of the bottom part 2 through the free space 9. The excessamount of compression, i.e., the difference between the outside diameterof the press fit surface 8 and the corresponding inside diameter of thetop part 3, in the press fit area 19, is roughly 0.1 mm to 0.3 mm,preferably 0.15 mm to 0.2 mm. FIG. 6 also shows the O-ring 11 which ispressed between the groove 10 of the bottom part 2 and the O-ring area22 of the top part 3.

Finally, it should be pointed out that, in this embodiment, both thestraight surfaces 6 of the bottom part 2 and also its curved surfaces 7have an angular periphery of roughly 30 degrees.

What is claimed is:
 1. A multipart housing for sensors comprising:abottom part as a process connection; and a top part as a componentreceiver which contains at least one half of electrical and electroniccomponents of the sensors; wherein the bottom part and the top part areconnected to one another by an elastic press fit and in an area of thepress fit there are straight surfaces and curved surfaces; and wherein afree space is formed between the top part and the bottom part in areaswhere the curved surfaces and the straight surfaces face each other. 2.A housing as claimed in claim 1, wherein the straight surfaces and thecurved surfaces form a press fit surface in an upper area of the bottompart.
 3. A housing as claimed in claim 2, wherein a groove is formed onthe bottom part underneath the press fit surface for holding an O-ring.4. A housing as claimed in claim 2, wherein a top edge of the bottompart defines an insertion cone above the press fit surface.
 5. A housingas claimed in claim 2, wherein part of the bottom part defines a keysurface having a graduation which is used as a support surface for thetop part.
 6. A housing as claimed in claim 5, wherein the bottom part isproduced by turning from standardized hexagonal solid material and partof an original surface of the hexagonal solid material forms the keysurface.
 7. A housing as claimed in claim 6, wherein the straightsurfaces are part of the original surface of the hexagonal solidmaterial.
 8. A housing as claimed in claim 7, wherein the straightsurfaces have an angular periphery of about 30 degrees.
 9. A housing asclaimed in claim 5, wherein corners of the key surface are rounded offand an outside diameter of the key surface is equal to an outsidediameter of the top part in an area of the corners.
 10. A housing asclaimed in claim 2, wherein a lower area of the bottom part has at leastone of an inside thread and an outside thread and the upper area of thebottom part has an inside thread.
 11. A housing as claimed in claim 2,wherein the curved surfaces have a greater angular periphery than thestraight surfaces.
 12. A housing as claimed in claim 2, wherein the toppart has the shape of a sleeve with a constant outside diameter and awall thickness of the top part decreases in a lower area thereof whichdefines a press fit area.
 13. A housing as claimed in claim 2, whereinthe difference between an outside diameter of the press fit surface anda corresponding inside diameter of the top part in the press fit area isroughly 0.1-0.3 mm.
 14. A housing as claimed in claim 2, furthercomprising a catch connection for coupling the bottom part and the toppart.
 15. A housing as claimed in claim 2, wherein the top part has ahole for a plug connection.
 16. A housing as claimed in claim 2, whereinthe bottom part and the top part are made of coated brass or uncoatedhigh quality steel.
 17. A housing as recited in claim 2, wherein thedifference between the outside diameter of the press fit surface and thecorresponding inside diameter of the top part in the press fit area isroughly 0.15-0.2 mm.